[Cairo] New functions for cairo_matrix

[Keith Packard]

Around 15 o'clock on Nov 14, Duncan Mak wrote:

> I needed an 'equals' function and an accessor to the elements in a
> cairo_matrix_t, so I wrote these two functions:

The equals function is probably fine, but the accessor exposes the 
underlying structure of the transformation perhaps more than we should.  

Can you tell us what you want to do with the elements?

-keith